This invention relates in general to a side load protection system for rotating equipment such as digger derricks and cranes.
Digger derricks, cranes, and other types of rotating equipment which are mounted to utility vehicles typically include a rotating turret from which a boom extends. The turret or boom is usually equipped with a winch having a line extending over a sheave on the outboard end of the boom. In the case of a digger derrick, an earth auger or earth anchor driving tool is mounted on the boom and provided with a motor and speed reducer. The boom is connected to the turret for up and down pivotal movement and is usually extensible and retractable so that its outboard end may be universally positioned to perform various digging or hoisting operations.
Typically, the rotation system for this type of equipment includes a hydraulic motor, a speed reducer with a pinion gear on the output shaft, and a large stationary bull gear on the frame to which the turret is rotatably mounted. A motor drives the pinion gear through the speed reducer, and this rotates the pinion around the bull gear to thereby rotate the turret and the boom. The speed reducer is often a self-locking type which may be driven from only the motor side and not from the opposite or pinion side.
A self-locking speed reducer has an inherent tendency to "step" when the boom is rotated down a grade. The "stepping" is caused by the self-locking or one-way nature of the speed reducer as it stops the boom rotation until the motor catches up with the boom and then allows the boom to start downhill again such that it runs ahead of the motor momentarily until stopped by the speed reducer, whereupon the stepping action is repeated.
In order to eliminate this objectionable stepping action and obtain a smooth boom rotation even when rotating down a grade, the recent trend has been to employ a non self-locking speed reducer mechanism which may be driven from either side; i.e., from the motor side as intended and also from the boom or pinion side in back driving fashion. With this type of speed reducer, the drive linkage requires a brake in order to stop the load when the boom rotation is stopped, and to normally prevent back driving under the influence of the load when the boom is not being rotated. The brake must be powerful in order to be able to quickly stop the boom when it is being rotated down a grade with substantial momentum. Also, the brake must be able to easily release when the boom is set into rotation by the drive motor.
Typically, the brake is a disc type brake which is spring biased such that it is normally engaged to prevent rotation of the boom. When the hydraulic rotation motor is activated to begin rotating the boom, hydraulic fluid is forced under pressure against a piston which releases the brake and thereby permits the boom to be driven. The primary problem with this type of brake arrangement is that it offers no protection against excessive side loading of the machine.
Excessive side loading can be applied to the boom when the winch is used to pull a heavy load in from the side of the boom rather than positioning the outboard end of the boom directly above the load. It can also be applied if an auger type digger "corkscrews" into the ground due to the application of excessive pressure in driving the auger at an angle from vertical. In addition, destructive side loading can result from improper installation of a screw type earth anchor which is driven into the ground by a special tool. These earth anchors screw themselves into the ground at an inclined angle under the influence of the driving tool. It is necessary for the digger operator to lower and swing the boom to the side as the earth anchor is being driven so that the boom will generally follow the path of the earth anchor. However, if he forgets or otherwise fails to do so, the earth anchor will tend to pull the boom to one side and thus exert considerable side loading on the machine.
The result of excessive side loading is often destruction of the boom, turret, or rotation deive mechanism. The boom is pulled in the direction of the load, and in the case of a non self-locking speed reducer this tendency is strongly resisted by the brake. The brake is powerful enough to permit the boom from back driving toward the load, and consequently, the boom bends, the gears in the drive system are stripped, or the turret is severely damaged.
It is an object of the present invention to provide, in a rotation drive system, a brake release arrangement which, whenever the external side loading on the equipment exceeds a preselected level, partially relaxes the brake force to permit slippage.
Another object of the invention is to provide a brake release arrangement of the character described which does not interfere with normal operation of the brake or drive system.
Yet another object of the invention is to provide a brake release arrangement of the character described that is adjustable as to the extent to which the brake releases when excessive side loading occurs. This adjustability feature permits setting of the brake release at a level where the brake slips just prior to the load level at which damage to the machine would occur, so that the machine is able to handle normal loads without slippage of the brake. Also, compensation is made for wear and other variations in the brake and other components of the drive linkage.
A further object of the invention is to provide a brake release arrangement of the character described that operates hydraulically in order to take advantage of the existing hydraulic system of the machine.
An additional object of the invention is to provide a brake release arrangement of the character described that operates only when the equipment that can cause side loading is operating. Since the brake release takes hydraulic fluid from the supply line to the digger and winch motors, it operates only when needed; i.e., when the digger or winch is operating to possibly overload the machine.
Still another object of the invention is to provide a brake release of the character described which is simple, reliable, and economical.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.